While the E3-1230 is cheaper, and newer, there's more power available using the older E5620 CPU. The big two items are the ability to scale the memory very high if needed, and the other (which is in my opinion more important) the ability to add a second CPU to the box increasing the number of threads per cores.
The E3-1230 has a maximum of ONE CPU allowed on the board, with 8MB L3 Cache
The E5620 can have TWO CPU's, giving it a huge boost in power and also uses 12MB L3 Cache - more memory available for the CPU means faster processing of data.
While not really a factor when it comes to this forum, the 1230 server has a maximum of 32GB memory allowed, whereas the E5620 can handle up to 288GB memory. Again, not really a determining factor as if we need 32GB of memory to run this forum, we surely need more than 1 CPU
Price is a factor, but should never be THE
determining factor when looking at data side by side in comparison to the requirements being met.
As it stands, the existing server that the forums are running on is a X3210 - so this is a HUGE jump forward.